The concept of analyzing wood using electromagnetic radiation has been suggested even well before any equipment capable of commercially utilizing such a concept was available, see for example, an article by D. G. Miller entitled "Detection of Rot in Wood by Electronic X-Ray Fluoroscopy" published in the British Columbia Lumberman of October 1964. The concept of using x-rays for detecting rot in wood was described as being old at that time and refers to an investigation as far back as 1929. The theory suggested that provided rot had progressed sufficiently to significantly reduce the density of the wood, the x-ray absorption would also be reduced. The article concludes that x-ray fluoroscopy provides a rapid nondestructive method of making internal inspections of wood for rot pockets and for metal.
An article entitled "Defect Detection in Lumber --State of the Art" by Szymani and McDonald in the November 1981 issue of Forest Products Journal, reviews the various techniques for analyzing board and logs. In relation to fluoroscopy, reference is made to the above article of Miller and to the real time x-ray, television and x-ray cinetography so that the images can be projected directly through a television network. Also described is a system where an x-ray sensitive device detects the amount of x-rays passing through the specimen and wherein by filtering and amplifying the signal, an indication of the presence or absence of defects could be provided and the output used via computer for lumber grading and sawing decisions. Particular attention is directed in this article to the Scintaflex System which directs, in this case neutrons at a point area on the board and senses the amount of radiation traversing the board to provide an indication of the density at the point.
Various techniques have been used or described to identify knots and/or rot in logs, for example, in the article "Locating Knots by Industrial Tomography--A Feasibility Study" by Taylor et al., published in the Forest Product Journal of May 1984 or in the article "A Computer Vision System that Analyzes CT-Scans of Saw Logs" by Funt and Bryant in a paper given at the IEEE Computer Society Conference on computer vision and pattern recognition.
Funt and Bryant have also published a paper entitled "Detection of Internal Log Defects by Automatic Interpretation of Computer Tomography Images" published in the January 1987 issue of the Forest Products Journal, which describes in detail the analysis of a log cross section histogram of a density map developed by a scan of a log using x-rays and the analysis of this histogram to determine the location of knots and rot.
Optical scanners have also been used to determine the location of surface defects in lumber by differentiating based on surface color.
Automatic lumber processing systems (ALPS) have also been described wherein the information derived from an optical scan of the board is analyzed based on tone, color, texture and pattern recognition to determine the location of surface defects in a piece of lumber and to use the information so generated to provide a sawing solution for sawing of the scanned board to obtain the optimum of recoverable lumber from the scanned board.
An article in IEEE "Transactions on Pattern Analysis and Machine Intelligence" Volume TAMI-5 No. 6 November 1983 entitled "Code Identifying and Locating Surface Defects in Wood--Part of An Automated Lumber Processing System" by Conners et al describes a system wherein an image is produced by optical scanning such as by means of a laser scan and then the image is examined to gauge its tonal properties, i.e. degree of brightness, its texture or pattern qualities and pattern recognition to detect defects in the lumber material and the position of these defects.
An article entitled "ALPS--Potential New Automated Lumber Processings System" by McMillin et al., in Forest Products Journal, Volume 34, No. 1, January 1984 deals with sensing and locating defects in a log and provides an optimum cutting solution based on this information. In this publication a log is processed by scanning using photon tomography and computer reconstruction of axial projections from three different angles to locate defects in the log. After sawing the log into boards, the boards themselves are scanned with video cameras and the image information digitized and analyzed for tonal and textural quality and an optimal cutting strategy based on the defect location is then implemented.
The article "A Prototype Software System Locating and Identifying Surface Defects in Wood" by Conners, given at the Seventh International Conference on Pattern Recognition in Montreal, Canada July 30-Aug. 2 1984 and published in the Proceedings Volume 1, provides further details on differentiating clear wood from defective wood in lumber utilizing optical scanning techniques wherein the background wane, knots and clearwood are distinguished.
U.S. Pat. No. 3,931,501 issued Jan. 6, 1976 to Barr et al discloses yet another scanning technique for determining and designating the surface defects on a piece of wood and then providing a cutting pattern for edging the wood into discreet lumber elements.
Canadian Pat. No. 1,146,051 issued May 10, 1983 to Strandberg et al describes a system for optimizing based on measuring the contours of a piece of timber and sawing based on an optimization program which positions the piece of timber for sawing in the edger and adjusts the edger accordingly.
Canadian Pat. No. 1,125,148 describes an optical sensor detecting irregularities along the lateral edges of a cant and adjusting the position of the cant for sawing to eliminate these irregularities.
It will be apparent from the above that a variety techniques have been suggested and provided in some cases for scanning boards to develop images of the surface of the board which are then analyzed first to determine defects and types of defects and location of these surface defects and then devise an optimum cutting solution for edging of the board and position the same for subsequent edging. These systems primarily utilize optical scanning techniques for providing the image to be analyzed, however it has been proposed to use in some cases electromagnetic radiation by directing a pinpoint of such radiation through the board and sensing the intensity of the radiation after it traverses the board to provide indications of the density.
Thus it is known in real time to provide analysis of a board and devise an optimum cutting solution, i.e. to analyze the images produced by scanning of the board in real time to determine the location of defects and from this generate an optimum cutting pattern. Such real time analysis have been based exclusively on optical scanning and analysis of the image so produced. However it will be apparent that optical scanning as such can determine only surface defects and in many cases is limited by the surface of the flitch being scanned so that the rough surface of a rough sawn flitch cannot be processed using this technique.
X-rays or electromagnetic detection techniques have been applied primarily to the analysis of the whole log rather than to a flitch or cant and the image (images) generated have been analyzed for defects and a cutting solution for logs. It has been suggested that x-ray tomography or fluoroscopy may be applied to detect defects in lumber. To date the published information relates to the use of x-rays to inspect wood and have not been of a practical nature, i.e. operated in real time (capable of operating at conventional production speeds).